19.4

The book is over...These are just exercises...

19.3

This part explained a bit more about quantum computing and how it works to do things in parallel by using a linear combination of states for the input and it gets a set of states as an output. I really still don't understand how this works or why. Also, I pretty much missed how the factoring algorithm works. I understand that they perform a fourier transform on the data points, but I'm not sure what the transform's result means in the context of finding a root.

19.1-19.2

I liked the intro to quantum cryptography since it explained how light is used and I found it quite fascinating. I thought it was interesting that they used the polarity as a measurement of the bit. I didn't understand how quantum security is more secure at all since someone could perform a man in the middle attack quite easily.

7.4-7.5

The Diffie-Hellman key exchange was a really nice surprise since it's so simple, and it's easy to understand how it works. I like how it seems like it would be easy to break, but in reality it's very very hard. I didn't understand the ElGamal crypto system. I'm not sure what they are trying to do in it, and it seems kind of strange. I see why it works with the identity, but I'm not sure on the rationale behind it.

6.6-6.7

I thought that the idea of using public key cryptography to confirm who sent a message is really neat idea since it allows you to use the encryption for verification. I never thought of using the private key to decrypt as a way of verifying who sent a message. It's really quite clever. I didn't quite grasp the example they used for the two countries and how that would work.